The present invention relates to a system and method for vacuum depositing thin film lavers on a substrate and more specifically to such a system and method in which plural layers are deposited on a substrate by sputtering to produce thin film magnetic recording discs and other products.
The deposition of films by sputtering is well-known in the art. Two exemplary types of sputtering are direct current sputtering, commonly designated as DC sputtering, and radio frequency sputtering, commonly designated as RF sputtering. DC sputtering is usually restricted to the deposition of conductive films. However, RF sputtering may be used to deposit conductive, dielectric or insulating materials. Sputter depositing of films is finding increasing applications. For example, in the fabrication of thin film magnetic recording discs for computers and in the manufacturing of semi-conductor devices.
One early approach for manufacturing multi-layer thin film magnetic discs involves plating aluminum substrates with a first layer of nickel phosphorus and with a second magnetic layer of cobalt phosphorus. These plated substrates are then placed in a deposition chamber and this chamber is evacuated. Thereafter, a layer of carbon, a wear resistant substance, is sputtered onto the substrates. The pressure in the chamber is then returned to ambient conditions and the substrates are removed.
The above approach suffers from a number of significant drawbacks. For example, with this procedure, the manufacture of discs is relatively time consuming. Furthermore, when the substrates are transferred to the deposition chamber, it is difficult to prevent contamination of the partially processed substrates. Contaminates such as oxygen and water vapor present serious corrosion and other problems. Moreover, with the above approach, it is difficult to produce thin film magnetic discs with consistently uniform magnetic properties from disc to disc. Therefore, the performance of such discs is somewhat unpredictable, particularly when used in high density data recording applications.
Another prior art thin film magnetic disc manufacturing apparatus has a single large vacuum deposition chamber within which a number of separate sputtering targets are provided. In this device, substrates are carried in a linear direction and at a constant speed through the deposition chamber. As the substrates travel through the chamber, they pass between successive pairs of sputtering targets which each sputter a layer of material onto the passing substrate. The thickness of the various sputtered layers is varied by adjusting the power delivered to the respective sputtering targets.
This apparatus, although somewhat faster than the previously described approach, also has a number of disadvantages. As one example, this apparatus has limitations in its capacity to optimize parameters which affect the effectiveness of sputtering of each particular layer. Such parameters include factors such as sputtering gas pressure, sputtering gas mixture, and the duration of sputtering. In addition, such prior art devices do not compensate for non-uniform sputtering by a target. For example, if a sputtering target is sputtering at a different rate from its upper region than from its lower region, a substrate traveling in a linear direction past the target is sputtered with a layer of uneven thickness.
Furthermore, maintenance of such devices is difficult and time consuming. That is, the entire deposition chamber is exposed to the ambient environment whenever a particular sputtering target is repaired or replaced. This exposes all of the sputtering targets to contamination. In addition, due to the size of the chamber, significant time is required to reestablish a high vacuum in the chamber following maintenance.
Therefore, a need exists for an improved system and method for vacuum depositing plural thin film layers on substrates and also for such a system and method which employs sputtering to produce thin film magnetic recording discs and other products.